IBM 6400 series Maintenance Manual page 136

All E's + FF A pattern of all E's repeated for ten lines and followed by a
form feed to the top of the next page. This test is useful for identifying
paper motion or paper feed problems.
Underlines An underline pattern useful for identifying hammer bank
misalignment.
136
Ribbon
Hammer bank cover
MPU sensor
Hammer springs
Hammer coils (shuttle frame assembly)
Hammer bank cover
Power supply board
Paper motion sensor or cable
Paper feed belt or motor
Splined shaft bearings
Tractors or tractor belts
Hammer bank cover
Hammer tips
Paper feed belt or motor
Splined shaft bearings
Tractor bearings or belts
Troubleshooting